Specs: Be more precise about how to decode UTF-8 and the implications thereof

sky/specs/parsing.md

 Parsing
 =======
 
 Parsing in Sky is a strict pipeline consisting of five stages:
 
 - decoding, which converts incoming bytes into Unicode characters
   using UTF-8.
 
 - normalising, which manipulates the sequence of characters.
 
@@ skipping 10 matching lines @@
 Later stages cannot affect earlier stages.
 
 When a sequence of bytes is to be parsed, there is always a defined
 _parsing context_, which is either an Application object or a Module
 object.
 
 
 Decoding stage
 --------------
 
-To decode a sequence of bytes _bytes_ for parsing, the [UTF-8
-decoder](https://encoding.spec.whatwg.org/#utf-8-decoder) must be used
-to transform _bytes_ into a sequence of characters _characters_.
+To decode a sequence of bytes _bytes_ for parsing, the [utf-8
+decode](https://encoding.spec.whatwg.org/#utf-8-decode) algorithm must
+be used to transform _bytes_ into a sequence of characters
+_characters_.
+
+Note: The decoder will strip a leading BOM if any.
 
 This sequence must then be passed to the normalisation stage.
 
 
 Normalisation stage
 -------------------
 
 To normalise a sequence of characters, apply the following rules:
 
 * Any U+000D character followed by a U+000A character must be removed.
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         there isn't one, skip this token.
      2. If there's a ``template`` element in the _stack of open
         nodes_ above _node_, then skip this token.
      3. Pop nodes from the _stack of open nodes_ until _node_ has been
         popped.
      4. If _node_'s tag name is ``script``, then yield until there
         are no pending import loads, then execute the script given by
         the element's contents.
 3. Yield until there are no pending import loads.
 3. Fire a ``load`` event at the _parsing context_ object.